Medical ventilators may determine when a patient takes a breath in order to synchronize the operation of the ventilator with the natural breathing of the patient. In some instances, detection of the onset of inhalation and or exhalation may be used to trigger one or more actions on the part of the ventilator.
The response performance of a medical ventilator to a patient-initiated triggering (transition from exhalation into inhalation) and cycling (transition from inhalation into exhalation) are important characteristics of a medical ventilator. A ventilator's triggering and cycling response impacts the patient's work of breathing and the overall patient-ventilator synchrony. In patient-initiated ventilation such as Pressure Support Ventilation (PSV), Proportional Assist Ventilation (PAV), etc., the airway pressure drops below the baseline and flow moves into the lung as a patient initiates an inspiratory effort. As the inhalation phase proceeds, the inspiratory flow decreases in accordance with the decreasing inspiratory effort by the patient. The ventilator detects the patient's inspiratory or expiratory effort and uses this information to provide ventilation therapy to the patient as set by the operator.
The triggering or cycling response performance of a ventilator is a function of a patient's respiratory behavior (which includes breathing effort magnitude and timing characteristics) as well as the ventilator's gas delivery dynamics and flow control parameters (actuator response, deadbands, etc.). In conventional flow triggering and cycling modality, the patient effort is detected based on the magnitude of expiratory and inspiratory flow changes generated by the patient respiratory effort. In conventional flow cycling modality, the cycling point (transition from inhalation into exhalation) is determined using the descending inspiratory flow and comparing it against peak inspiratory flow and a set percent threshold. Inspiratory flow is sensed by the computation of the ventilator net flow (estimated lung flow) and compared against a set trigger sensitivity value for triggering or a set percentage of peak inspiratory flow for cycling.